Magnetic contact



July 13, 1943.v A. H. LAMB 2,324,262

MAGNETIC CONTACT Fued March 1, 1941 J6 /3 Ag. 6I

Patented July 13, 1943 MAGNETIC CONTACT Anthony H. Lamb, Elizabeth, N. J., assignor to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New Jersey Application March 1, 1941, Serial No. 381,326

Claims.

This invention pertains to contacts for instrument type relays and more particularly to relay contacts of the magnetic type.

Conventional type contacts, as presently used on instrument type relays having a high electrical sensitivity, present a serious problem, as the quality of the contact closure decreases rapidly with the number of times that the contact is established and broken. The torque supplied by the movable element of such relays is insuiiicient to establish enough Contact pressure to insure a good electrical Contact under normal operating conditions. When the condition of the circuit in which the relay is connected is such that the relay contacts are caused to close under light pressure, considerable chattering of the contacts takes place. This chattering is accentuated by normal mechanical vibrations of the relay and becomes acute in alternating current relays wherein the movable element of the relay tends to follow the cycles of the alternating current wave. Such chattering results in rapid destruction of the contacts even when elaborate precautionary measures are employed.

Magnetic contacts of the type disclosed in my Patents 2,014,385 and 2,014,336 have eiiectively solved the problem of contact chattering. Such contacts, however, require some means for resetting or separation after contact closure as the movable element of the sensitive relay is incapable of supplying suicient torque for this purpose. Auxiliary devices, or a second relay with magnetic contacts of the prior type, have been required in relay systems of the type in which control actions in opposite sense are to be effected when the magnitude of the measured factor exceeds or falls below a preselected control range.

In temperature control systems, for example, the instrument relay may close a controlled circuit which opens a fuel supply valve when the temperature falls to a preselected low value, and may open the controlled circuit when the temperature rises to a preselected high value. Simple instrument type relays can be used for a control over a preselected range between high and low measured values if the measured iactor develops suflicient force to ensure reliable contact closures, but the magnetic contacts of prior-sensitive relays have prevented an automatic separation of the contacts when the value of the measured factor varies over the preselected control range.

It is an object of this invention to provide mag- :netic contacts of suilicient magnetic strength to prevent chattering of the contacts, and which do (Cl. 20G- 166) not require auxiliary means for resetting. Another object of this invention is the provision of relay contacts of the magnetic type which are attracted and establish a reliable Contact closure by magnetic pull but which may be separated by the torque of the movable element of the relay. Another object is the provision of magnetic type contacts provided with a covering of material having good electrical contacting qualities, whereby upon closure of the contacts the actual magnetic materials forming the contacts will be separated by a denite non-magnetic gap, of constant or of adjustable length, that determines the effective control range of the relay.

These and other objects of the invention will be apparent from the following specification when taken with the accompanying drawing. The drawing is for purposes of illustration and is not to be construed as deiining the limits of the invention, reference being had for this purpose to the appended claims.

In the drawing wherein like characters denote like parts in the several figures:

Fig. l is a diagrammatic View of an embodiment'l of the invention in a relay having one movable and one stationary Contact of the magnetic type;

Fig. 2 is a curve sheet showing the variation in the holding power of the closed contacts with the length of the non-magnetic gap;

Fig. 3 is a fragmentary view, partly in section and on an enlarged scale, of magnetic contacts made in accordance with this invention;

Figs. 4, 5, 6 and 7 are similar fragmentary enlarged scale views showing other embodiments of the invention;

Fig. 8 is a fragmentary view, partly in section, of a construction which permits adjustment of the non-magnetic gap after the contacts have been assembled into a relay; and

Fig. 9 is a fragmentary and diagrammatic View of an embodiment that includes means for aiding the movable element of the relay in separating the magnetic contacts.

A direct current relay as shown somewhat diagrammaticaily in Fig. 1, has a permanent magnet i and a movable coil 2 to which a pointer or contact arm 3 is secured in any suitable manner. When the pointer 3 is provided with a soft iron rider 4 for cooperation with a magnetized contact as described in my prior patents, some mechanical means is required for the resetting or separation vof the contacts as the magnetic attraction between them is greater than can be overcome bythe torque of the .movable coil 2.

According to this invention, the magnetized contact comprises a miniature bar magnet 5 arranged with its axis substantially in the arcuate path of the soft iron contact 4 and carrying a contact tip 6 of non-magnetic material, such as silver, gold, platinum-iridium or the like, for engagement with the contact 4 of the relay pointer. The circuit controlled by the relay may be of any desired ytype including, for example, a current source 'I and auxiliary relay 8 with normally open contacts S that close when the magnetic rider 4 engages the contact tip E of the magnetized contact system. The pointer 3 ci the instrument relay moves along a scale I that is graduated in any desired or appropriate numerical values or symbols. In the particular embodiment shown in Fig. Il, the scale I0 is graduated in voltage values of an effective control range of from 6.0 to 6.4 volts.

The eifective magnetic eld or pull of the magnet 5 extends towards the magnetic rider over a distance a and, when the measured voltage falls to 6.0 volts, the current flow through the coil 2 displaces the magnetic body 4 into the illustrated position, at the distance a from the tip of the magnet 5. The magnetic pull then overcomes the torque developed by the current flow in the coil 2, and the magnetic body 4 is drawn towards the magnet with a progressively increasing force and strikes the contact tip 6 with sufficient momentum to break through any film of oxide or dirt that may have formed on the contact surfaces.

The magnetic attraction is not aected to any appreciable extent by the length b of the nonmagnetic contact tip 6 that is located between the magnet 5 and the magnetic rider 3 of the relay pointer 2. lThe pull-in value or lower limit of the control range of the illustrated relay is therefore independent of the length of the non-magnetic gap established between the cooperating magnetic elements of the contact system. The break away value or upper limit of the control range is determined, however, by the length b of the non-magnetic gap. The relation between the holding power of the closed contacts and the length of the non-magnetic gap is shown graphically by curve A of Fig. 2.

The maximum holding power is developed when little or no magnetic gap is present, as in the magnetic contacts of my prior patents that were bare or plated with silver or gold lms of a thickness of about 0.0001 inch or less. The holding power falls off as the non-magnetic gap b is increased and becomes zero when the gap increases to the value a equal to the maximum effective range of the magnetic attraction. The length of the non-magnetic gap b will be substantially less than the magnetic attraction range a in all practical embodiments of the invention, but will be sufficient to reduce the magnetic holding power to a value that can be overcome by the torque developed by current flow through the coil 2.

The method of operation of the novel magnetic contacts will be apparent from the following discussion of an application of the invention to the control of a battery charging system. Assuming that the normal battery voltage is 6.2, the relay may be set to establish contact when the voltage drops to 6.0. Closure of the relay contacts 4, E energizes the auxiliary relay 8 and sets the charging device into operation, whereupon the voltage across the relay increases to say 6.1. This voltage increase tends to separate the relay contacts, but the magnetic attraction between the permanent magnet 5 and the iron rider 4 prevents the contacts from opening. The non-magnetic gap between magnet 5 and rider 4, as established by the contact tip 6, may be predetermined by proper selection of the length b of the contact tip 6 so that the battery charging voltage must increase to say 6.4 volts before the contacts will separate. Upon separation of the contacts, the auxiliary relay 8 is de-energized and the charger will be disconnected from the circuit, and the voltage of the battery will return to its normal value, namely 6.2.

As shown in Fig. 3, the rider on the movable contact arm 3 comprises a soft iron body 4 that carries a thick layer II of a non-magnetic metal of good electrical conductivity, for example silver, that may be readily electroplated upon the iron rider. The cooperating magnetized contact may comprise a small permanent magnet 5a that has a similar thick plating 6a of a metal, such as silver, of high electrical conductivity. The non-magnetic gap may have a length of from about 0.001 to 0.2 inch, depending upon the desired value for the holding power of the magnetic system, and the platings 5a, and I l may be of the same or of different thickness.

The diiiiculty of providing a uniform plating of a given thickness makes the above described construction suitable for instruments where a denitc separating torque is not required.

When it is desirable to construct contacts of this type which will require a denite amount of force for separation, an embodiment such as shown in Fig. 4 is preferable. A contact button or rivet I2 of a suitable Contact material, such as silver, platinum-iridium, or the like, is force tted or threaded into the end of the permanent magnet 5 for engagement by the rider 4 of the contact arm. The thickness of the rivet head may be held to close manufacturing tolerances so that all relays provided with contacts of this type will require substantially the same amount of torque for resetting.

Another embodiment of the invention, as shown in Fig. 5, comprises the magnet 5b upon which a contact button or a cap I3 of suitable nonrnagnetic material is force iitted. Alternatively, as shown in Fig. 6, the non-magnetic cap I4 may be threaded upon the end of the magnet 5c.

A modication of the Fig. 4 construction, as illustrated in Fig. 7, includes a spacing washer I5 of any suitable non-magnetic material between the magnet 5 and the Contact rivet I 2,V the washer serving to increase the non-magnetic gap. The cooperating contact may be a coated or uncoated soft iron rider 4 or, as shown, a similar contact rivet i6 of non-magnetic material and a soft iron washer il may be provided on the relay pointer 3'. When the contacts are closed, the non-magnetic separating gap is represented by the thickness of the two rivet heads and the spacing washer I5.

It is sometimes desirable to readjust the length of the separating gap after the contacts have been assembled into a relay. This is possible with the construction shown in Fig. 8, wherein a non-magnetic screw I8, provided with a contact tip I9 of silver or the like, is threaded axially through the bore of the permanent magnet 5d.

To meet desired conditions it may sometimes be necessary to provide for a strong magnetic attraction between the permanent magnet and the iron rider. Under such conditions, the movable coil of the relay may not be capable of supplying,T sufcient torque to reset the contacts. To reset the contacts under such circumstances, a coil 2t may be disposed about the permanent magnet contact, which may be of any of the described types, to establish a temporary electromagnetic iield opposing that of the permanent magnet, thereby to permit separation oi the contacts. The flow of current to coil 2i) from a direct current source 2l is controlled by a manually operable resetting switch 22.

Having now described my invention, it will be apparent to those skilled in the art that further variations and modifications are possible. It will be understood that the permanent magnet may be attached to the pointer 3 and that the stationary Contact may then be made of soft iron. Or, the stationary contact and the movable contact may beth be permanent magnets. Further, the invention is not limited to sensitive relays, but is applicable to any device wherein positive contact closure is required Without necessitating auxiliary means for resetting.

I claim:

1. A Contact assembly for cooperation with a magnetic material Contact of a sensitive relay, said assembly comprising an element of magnetic material, and a contact tip of non-magnetic material adjustably mounted on and extending beyond said element toward the cooperating Contact.

2. In an electrical contact system for a sensitive relay, an element of magnetic material having an axial bore, a non-magnetic member extending through said bore and adjustable axially of said element, and a Contact tip on said nonmagnetic member.

3. A contact assembly for cooperation with a magnetic material contact of a sensitive relay, said assembly comprising an elongated element of magnetic material arranged with its axis substantially in the path of movement of the cooperating contact, a Contact tip of non-magnetic material, and means mounting said contact on said element for adjustment axially thereof.

A contact assembly as recited in claim 3, wherein said mounting means comprises cooperating threaded surfaces on said contact tip and said element.

5. In an electrical contact system for a relay,

* an element of magnetic material, and a contact cap of non-magnetic material adjustably mounted upon and extending across the end of said magnetic material element.

ANTHONY H. LAMB. 

